Nationwide, more than 8.4 million children (6-14yrs) attend afterschool programs (ASP, 3-6pm) for an average of 8hrs/wk, with the majority from low-income households. Because ASPs have such extensive reach and contact with children, national, state, and local organizations have called on them to help combat the epidemic of childhood obesity through policies targeting physical activity and healthy snacks. Two policies that have the greatest potential for widespread implementation and impact are the State of California's legislation (Proposition 49), which mandates that children attending state-funded ASPs should accumulate e30 minutes of moderate-to-vigorous physical activity (MVPA) daily during the program, and the Harvard nutrition guidelines for snacks, which require serving fruits and vegetables (FV) each day and restricting foods with added sugars (e.g., soda). While these public health policies are a necessary catalyst for promoting healthier behaviors, what is not known is what resources and strategies are needed to successfully achieve these policy goals. To date, there are few effective, low-cost strategies ASPs can adopt to meet physical activity and nutrition policy goals. Without effective strategies, it is unlikely such policies will accomplsh their intended purpose - increased daily MVPA and serving nutritious snacks. Our long-term goal is to advance the adoption and successful implementation of policies that promote physical activity and nutrition in ASPs nationwide. Our objective here is twofold. First, we will test the effectiveness of two promising strategies 1) professional development training designed to increase the amount of physical activity children accumulate while attending an ASP and 2) a site-level intervention that focuses on altering purchasing decisions and reducing price barriers to improve the quality of snacks children consume. This represents a fundamental step in establishing practice-based guidelines for the uptake and achievement of public health policy goals (CA and Harvard). We will use a 3-year delayed treatment, cluster randomized controlled trial design with 20 ASPs that serve mostly low-income and minority children (approximately 1300 children ages 6-12yrs) in Columbia, SC and address the following specific aims: Aim 1. Evaluate the impact of a staff-level intervention, a professional development training program focused on core competencies to promote physical activity, on children's physical activity levels; Aim 2. Evaluate the impact of a site-level intervention, a snack modification program that includes a discount buying program, on the quality of snacks served and consumed; and Aim 3. Evaluate the implementation of the staff-level and site-level interventions and identify organizational, staff, and setting characteristics that influence the process of implementing these strategies. This study is innovative because limited information exists on effective strategies ASPs can use to achieve important public health policy goals. The proposed research is significant because our findings will strengthen the scientific knowledge-base regarding the implementation of these strategies in real-world settings to meet important policy goals.